Assessment of Early Successional Arthropod and Breeding Bird Response to Intercropping Switchgrass Within an Intensively Managed Loblolly Pine Forest

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5-1-2016

Assessment of early successional arthropod and breeding bird response to intercropping switchgrass within an intensively managed loblolly pine forest

Craig Daniel Marshall

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Assessment of early successional arthropod and breeding bird response to intercropping

switchgrass within an intensively managed loblolly pine forest

By TITLE PAGE Craig Daniel Marshall

A Thesis Submitted to the Faculty of Mississippi State University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Forest Resources in the Department of Wildlife, Fisheries, and Aquaculture

Mississippi State, Mississippi

May 2016

2016

Assessment of early successional arthropod and breeding bird response to intercropping

switchgrass within an intensively managed loblolly pine forest

By APPROVAL PAGE Craig Daniel Marshall

Approved:

______Scott A. Rush (Major Professor)

______Darren A. Miller (Committee Member)

______Kristine O. Evans (Committee Member)

______JoVonn G. Hill (Committee Member)

______Kevin M. Hunt (Graduate Coordinator)

______Andrew J. Kouba (Department Head)

______George M. Hopper Dean College of Forest Resources

Name: Craig Daniel Marshall ABSTRACT Date of Degree: May 6, 2016

Institution: Mississippi State University

Major Field: Forest Resources

Major Professor: Scott A. Rush

Title of Study: Assessment of early successional arthropod and breeding bird response to intercropping switchgrass within an intensively managed loblolly pine forest

Pages in Study 47

Candidate for Degree of Master of Science

Loblolly pine (Pinus taeda) plantations are a common land use of the southeastern

United States that have the potential to function as a source of cellulosic biomass for biofuel production. A novel land use practice of intercropping switchgrass (Panicum virgatum) between planted loblolly pines has been developed as a potential method of cellulosic biomass production. I evaluated response of arthropods and breeding birds to intercropping switchgrass within loblolly pine plantations compared to typically managed pine plantations. I detected 13 arthropod orders and 44 breeding bird species during 2014

– 2015. Intercropping switchgrass reduced arthropod diversity and evenness, with richness not affected. Arthropod abundance response to intercropping switchgrass varied

among orders. Breeding bird species did not respond differently to intercropping

switchgrass compared to typically managed pine. Continued assessment is needed to provide greater insight regarding potential effects of this land use practice throughout a rotational period.

DEDICATION

To my father, whose guidance and love molded me into the man I am today. To

Sam Riffell and Scott Rush, for your support, guidance, and patience. To the love of my life, Jenny Foggia. And finally, to Miko, for your unwavering loyalty, support, and love.

ACKNOWLEDGEMENTS

I would like to thank my committee, Dr. Sam Riffell, Dr. Scott Rush, Dr. Darren

Miller, Dr. Kristine Evans, and Dr. JoVonn Hill, for the opportunity to pursue graduate studies and their support and guidance throughout the pursuit of my Master’s degree. I am eternally grateful for the support and friendship of former and current graduate students, thank you. Thank you to Weyerhaeuser Company, Catchlight Energy, LLC, and the College of Forest Resources at Mississippi State University for providing funding for this project.

iii

TABLE OF CONTENTS

DEDICATION ...... ii

ACKNOWLEDGEMENTS ...... iii

LIST OF TABLES ...... vi

CHAPTER

I. NOVEL LAND USE PRACTICE FOR PRODUCTION OF SWITCHGRASS BIOMASS, A REVIEW ...... 1

Introduction ...... 1 Literature Cited ...... 4

II. ARTHROPOD RESPONSE TO INTERCROPPING SWITCHGRASS WITHIN LOBLOLLY PINE PLANTATIONS ...... 6

Introduction ...... 6 Materials and Methods ...... 9 Study Area ...... 9 Study Design ...... 9 Statistical Analysis ...... 12 Results ...... 13 Discussion ...... 14 Management Implications ...... 17 Literature Cited ...... 21

III. BREEDING BIRD RESPONSE TO INTERCROPPING SWITCHGRASS WITHIN A LOBLOLLY PINE PLANTATION ...... 25

Introduction ...... 25 Materials and Methods ...... 27 Study Area ...... 27 Study Design ...... 28 Statistical Analysis ...... 30 Results ...... 32 Discussion ...... 33 Management Implications ...... 36 iv

Literature Cited ...... 38

IV. GENERAL CONCLUSIONS ...... 42

Literature Cited ...... 45

LIST OF TABLES

2.1 Mean and standard deviation of arthropod abundance among treatments established within an intensively managed loblolly pine forest and summed across years (2014 – 2015) in Kemper County, Mississippi, USA...... 19

2.2 Linear tests of hypotheses of arthropod diversity, richness, and evenness among treatments established within a loblolly pine plantation in Kemper County, Mississippi, USA, 2014 – 2015...... 19

2.3 Linear tests of hypotheses of Araneae, Coleoptera, Diptera, Hemiptera, and Orthoptera abundance among treatments within a loblolly pine plantation in Kemper County, Mississippi, USA, 2014 – 2015...... 20

3.1 Mean and standard deviation of breeding birds detected per treatment and summed across years (2014 – 2015) within a loblolly pine plantation in Kemper County, Mississippi, USA...... 37

CHAPTER I

NOVEL LAND USE PRACTICE FOR PRODUCTION OF SWITCHGRASS

BIOMASS, A REVIEW

Introduction

Finite reserves of fossil fuels, concerns regarding energy security, and environmental costs associated with fossil fuel production and use have led to an increased interest in renewable energy sources (McLaughlin et al. 1999, Koh and

Ghazoul 2008). In particular, production of biofuels from cellulosic biomass, such as willows (Salix spp.), giant miscanthus (Miscanthus x giganteus), agricultural residues, and switchgrass (Panicum virgatum), have garnered considerable attention (Sanderson et al. 2006, Heaton et al. 2008). Depending on how they are cultivated and refined, biofuels

produced from cellulosic biomass can serve as an alternative energy source to fossil fuels,

which may reduce greenhouse gas emissions and contribute to conserving biological

diversity (Fargione et al. 2008, Koh and Ghazoul 2008, Fletcher et al. 2011). However,

the raw materials involved in biofuel production require either a significant redirection of

land used for agricultural production or conversion of land currently in a natural state

(Hoekman 2008, Broch et al. 2013). Novel land use practices and techniques, such as

producing biofuels from biomass grown on marginal land or from waste biomass, must

be developed for biofuels to significantly contribute to current and future energy needs

(Fargione et al. 2008).

Loblolly pine (Pinus taeda) plantations are a common landscape in the

southeastern United States and are a potential source of cellulosic biomass to produce

biofuels (Riffell et al. 2011, Verschuyl et al. 2011, Wear and Greis 2012). A recently

developed land use practice for cellulosic biomass production within loblolly pine

plantations is intercropping switchgrass between young pine trees (Riffell et al. 2012).

Switchgrass intercropping within loblolly pine plantations potentially reduces the amount

of land required for cellulosic biomass production. This practice also creates a system

that produces an annual source of switchgrass biomass during early rotation and

marketable forest products from mature pines (Riffell et al. 2012). A secondary benefit

associated with this land use practice is using native perennial grass, as opposed to its

non-native counterparts, such as giant miscanthus and reed canary grass (Phalaris

arundinaceae; Casler et al. 2009). Research has shown that planting switchgrass in North

America is a potentially viable land use practice for producing cellulosic biomass, while

maintaining biological diversity (Riffell et al. 2012, Robertson et al. 2012), whereas

minimal knowledge currently exists on how introduction of a non-native, potentially

invasive species, such as miscanthus, for producing cellulosic biomass will impact native

flora and fauna (Robertson et al. 2012).

Loblolly pine plantations of the southeastern United States support a diverse array

of flora and fauna, including species of conservation concern (Miller et al. 2009, Riffell

et al. 2011). Maintaining biological diversity, among other things, within these systems is

an integral aspect of forest management requirements set by sustainable forestry

certification programs, such as the Sustainable Forestry Initiative (Miller et al. 2009,

Sustainable Forestry Initiative Inc. 2010). Limited knowledge currently exists on how

intercropping switchgrass affects floral and faunal communities associated with loblolly pine plantations (e.g. Riffell et al. 2012, Homyack et al. 2013, Homyack et al. 2014,

Loman et al. 2014, King et al. 2014). Further, no study has yet to evaluate response of arthropod communities to intercropping switchgrass within loblolly pine plantations at any point throughout a rotational period.

With these research needs in mind, my objectives were to quantify response of arthropods and breeding birds to intercropping switchgrass within loblolly pine plantations, four and five years post-stand establishment. This study sheds light on how arthropods, an underrepresented taxonomic group within switchgrass intercropping

research, and breeding birds respond to within-stand alterations to vegetative

communities resulting from intercropping switchgrass. This study also adds to the current

body of literature evaluating effects of switchgrass intercropping on multiple taxonomic

groups, improving our overall understanding of this novel land use practice, and

providing necessary information for informed sustainable forestry management decisions.

Literature Cited

Broch, A., S.K. Hoekman, and S. Unnasch. 2013. A review of variability in indirect land use change assessment and modeling in biofuel policy. Environmental Science & Policy 29: 147 – 157.

Casler, M.D., J.H. Cherney, and E.C. Brummer. 2009. Biomass yield of naturalized populations and cultivars of reed canary grass. Bioenergy Research 2: 165 – 173.

Fargione, J., J. Hill, D. Tilman, S. Polasky, and P. Hawthorne. 2008. Land clearing and the biofuel carbon debt. Science 319: 1235 – 1238.

Fletcher Jr., R.J, B.A. Robertson, J. Evans, P.J. Doran, J.R.R. Alavalapati, and D.W. Schemske. 2011. Biodiversity conservation in the era of biofuels: risks and opportunities. Frontiers in Ecology and the Environment 9: 161 – 168.

Heaton, E.A., F.G. Dohleman, and S.P. Long. 2008. Meeting US biofuel goals with less land: the potential of Miscanthus. Global Change Biology 14: 2000 – 2014.

Hoekman, S.K. 2008. Biofuels in the U.S. – challenges and opportunities. Renewable Energy 34: 14 – 22.

Homyack, J.A., Z. Aardweg, T.A. Gorman, and D.R. Chacraft. 2013. Initial effects of woody biomass removal and intercropping switchgrass (Panicum virgatum) on herptofauna in eastern North Carolina. Wildlife Society Bulletin 37: 327 – 335.

Homyack, J.A., K.E. Lucia-Simmons, D.A. Miller, and M. Kalcounis-Rueppell. 2014. Rodent population and community responses to forest-based biofuel production. The Journal of Wildlife Management 78: 1425 – 1435.

King, K.L., J.A. Homyack, T.B. Wigley, D.A. Miller, and M.C. Kalcounis-Rueppell. 2014. Response of rodent community structure and population demographics to intercropping switchgrass within loblolly pine plantations in a forest-dominated landscape. Biomass and Bioenergy 69: 255 – 264.

Koh, L.P. and J. Ghazoul. 2008. Biofuels, biodiversity, and people: Understanding the conflicts and finding opportunities. Biological Conservation 141: 2450 – 2460.

Loman, Z.G., S.K. Riffell, B.R. Wheat, D.A. Miller, J.A. Martin, and F.J. Vilella. 2014. Breeding bird community response to establishing switchgrass in intensively- managed pine stands. Biomass and Bioenergy 67: 201 – 211.

McLaughlin, S., J. Bouton, D. Bransby, B. Conger, W. Ocumpaugh, D. Parrish, C. Taliaferro, K. Vogel, and S. Wullschlegar. 1999. Developing switchgrass as a bioenergy crop. Pages 282 – 299 in Perspectives on New Crops and New Uses. ASHS Press, Alexandria, Virginia, USA.

Miller, D.A., T.B. Wigley, and K.V. Miller. 2009. Managed forests and conservation of terrestrial biodiversity in the southern United States. Journal of Forestry 107: 197 – 203.

Riffell, S., J. Verschuyl, D. Miller, and T.B. Wigley. 2011. A meta-analysis of bird and mammal response to short-rotation woody crops. Global Change Biology Bioenergy 3: 313 – 321.

Riffell, S., J. Verschuyl, D. Miller, and T.B. Wigley. 2012. Potential biodiversity response to intercropping herbaceous biomass crops on forest lands. Journal of Forestry 110: 42 – 47.

Robertson, B.A., R.A. Rice, T.S. Sillett, C.A. Ribic, B.A. Babcock, D.A. Landis, J.R. Herkert, R.J. Fletcher Jr., J.J. Fontaine, P.J. Doran, and D.W. Schemske. 2012. Are agrofuels a conservations threat or opportunity for grassland birds in the United States? The Condor 114: 679 – 688.

Sanderson, M.A., P.R. Adler, A.A Boateng, M.D. Casler, and G. Sarath. 2006. Switchgrass as a biofuels feedstock in the USA. Canadian Journal of Plant Science 86: 1315 – 1325.

Sustainable Forestry Initiative Inc. 2010. Sustainable Forestry Initiative® (SFI) Standard, 2010 – 2014 Edition. American Forest and Paper Association. Washington, DC, USA.

Wear, D.N. and J.G. Greis. 2012. The southern forest futures project: summary report. 2011. United States Forest Service, General Technical Report SRS-168, Asheville, North Carolina, USA.

Verschuyl, J., S. Riffell, D. Miller, and T.B. Wigley. 2011. Biodiversity response to intensive biomass production from forest thinning in North American forests – a meta-analysis. Forest Ecology and Management 261: 221 – 232.

CHAPTER II

ARTHROPOD RESPONSE TO INTERCROPPING SWITCHGRASS WITHIN

LOBLOLLY PINE PLANTATIONS

Introduction

Forests cover approximately 245 million acres in the southern United States, with

44 million acres comprised of planted loblolly pine (Pinus taeda: USDA Forest Service

2007, USDA Forest Service 2012). Within Mississippi, loblolly pine covers an estimated

5 million acres (USDA Forest Service 2007). Loblolly pine plantations are economically beneficial to society by producing wood and wood fiber, while also providing other societal benefits through ecosystem services, such as protecting water quality, carbon sequestration, providing wildlife habitat, conservation of biological diversity, and recreation (Wigley et al. 2000, Miller et al. 2009). These benefits are derived from current management practices resulting in a heterogeneous landscape of varying successional stages and diverse plant communities at the landscape and patch level

(Miller et al. 2009).

With increased global interest in alternative energy sources, forest managers have

implemented a novel land use practice of intercropping switchgrass within loblolly pine

plantations (Koh and Ghazoul 2008, Riffell et al. 2012). This practice is aimed to produce

a renewable source of cellulosic biomass for biofuel production alongside production of

timber products. Implementing switchgrass intercropping within loblolly pine plantations

will result in changes to current management practices to facilitate switchgrass cultivation (Loman et al 2013). With regards to stand establishment, intercropping requires a more extensive removal of coarse woody debris from inter-bed rows and application of herbicide to facilitate switchgrass establishment (Loman et al. 2013, Wheat

2015). Congregation, addition, or loss of coarse woody debris due to switchgrass establishment may affect species associated with these fossorial microhabitat structures

(Ulyshen and Hanula 2009, Riffell et al. 2011, Loman et al. 2013). The prevention of

early successional and scrub-shrub vegetation establishment within inter-bed rows

through herbicide application and its replacement with switchgrass may alter the structure

and composition of the vegetative community at the stand level, resulting in changes in

biological diversity (Tews et al. 2004, Iglay et al. 2012a, Wheat 2015).

Past studies reveal that intercropping switchgrass within loblolly pine plantations

resulted in observed differences in ecological patterns, depending on the taxonomic group

and temporal scale studied (e.g. Homyack et al. 2013, Loman et al. 2014, Wheat 2015).

Wheat (2015) observed an initial reduction in plant community richness and diversity after stand and switchgrass establishment, whereas, Iglay et al. (2012a) found that intercropping switchgrass diversified the plant community in stands ≥ 5 years post-

establishment. Homyack et al. (2013) observed no short-term effects on herpetofauna

diversity or relative abundance from intercropping switchgrass within loblolly pine

plantations. Switchgrass intercropping research has covered multiple vertebrate taxa (e.g.

small mammals) and plants; however, research assessing response of arthropods to

switchgrass intercropping is lacking (e.g. Iglay et al. 2012a, Homyack et al. 2014).

Arthropods are well-suited for diversity studies, as they fulfill a variety of functional roles (e.g. pollinators, herbivores, predators, and decomposers) and are sensitive to changes in environmental conditions (bioindicators; e.g. Kremen et al. 2002,

Rainio and Niemela 2003, Rand and Louda 2006, Nummelin et al. 2007). Alterations to arthropod community structure may have direct and indirect effects on trophic dynamics, as arthropods are an important food resource for other organisms (Hamilton 1941,

Holmes and Schultz 1988, McCracken and Tallowin 2004, Landis and Werling 2010).

Observing how ecological patterns of arthropods are affected will provide a basis for future research aimed at assessing implications of intercropping switchgrass within loblolly pine plantations. Because arthropods are sensitive to environmental changes and because limited knowledge currently exists regarding arthropods and switchgrass

intercropping, I investigated arthropod community responses to intercropping switchgrass

within loblolly pine plantations. My objective was to assess responses of arthropod

diversity, richness, evenness, and abundance to intercropping switchgrass within loblolly

pine stands, four and five years post-establishment. I hypothesized that switchgrass

intercropping would decrease arthropod diversity, richness, evenness, and abundance

compared to loblolly pine stands, following typical management practices. Switchgrass

establishment in inter-bed rows would result in less available habitat for arthropods

associated with scrub-shrub vegetative communities, which is a common vegetative

assemblage of loblolly pine stands four and five years post-establishment (Iglay et al.

2012a, Foggia 2015, Wheat 2015).

Materials and Methods

Study Area

I collected arthropod data in Kemper County, Mississippi, USA (32 51’ N, 88 33’

W) within the Interior Flatwoods Area of the Upper Coastal Plain (Petty 1977) on property owned and managed by Weyerhaeuser Company, and within research sites established and maintained by Weyerhaeuser Company and Catchlight Energy LLC

(CLE), a joint venture between Chevron and Weyerhaeuser. The climate of the region was subtropical with mean annual temperatures of 16° C – 18° C (minimum and maximum) and a mean annual precipitation of 140 cm (National Oceanic and

Atmospheric Administration 2013). The study area consisted of 9,600 ha of loblolly pine stands of various ages (70%), mature pine-hardwoods (17%), hardwoods (10%), and non- forested areas (3%; Iglay 2010).

Study Design

My study followed a complete randomized block design consisting of five sampling blocks. Within each block, there were three; 10-ha experimental stands with randomly assigned treatments (pine control, switchgrass intercropped, and switchgrass monoculture). Each experimental stand was previously a mature loblolly pine stand clearcut harvested during 2009 and 2010. Pine control treatments used Weyerhaeuser standards for site preparation, competition control, tree planting, and tree spacing. Site preparation included a V-blade plow, bedding plow, and subsoil ripper to establish pine beds. Planted pine seedlings were spaced 1.5×6.1 m resulting in pine beds and inter-bed rows having widths of 1.2 m and 4.9 m, respectively. A banded application of imazapyr

(0.29 L/ha; Arsenal® AC, BASF Corp., Research Triangle Park, NC) and sulfometuron- 9

methyl (0.15 L/ha; Oust®, E. I. du Pont de Nemours and Company, Wilmington, DE)

was applied during the first growing season to pine beds to reduce woody and herbaceous

competition. Switchgrass intercropped treatments had similar site preparation as pine

control stands, with the addition of more extensive coarse woody debris removal. Once pine beds were established, a V-blade plow was used to remove coarse woody debris

from inter-bed rows into pine bed edges. Upon clearing inter-bed rows, a banded

application of glyphosate (2.34 – 4.68 L/ha; Accord®XRT, Dow AgroSciences,

Indianapolis, IN) was applied to inter-bed rows. Inter-bed rows were then disked and

broadcast seeded with switchgrass. Switchgrass intercropped stands were seeded in

spring 2011 and reseeded again in 2012, due to poor establishment after initial seeding.

Inter-bed rows were sprayed with a banded application of glyphosate and disked a second

time during the reseeding event in 2012. Site preparation for switchgrass monoculture

treatments included complete removal of coarse woody debris using a V-blade plow and

broadcast application of glyphosate (2.34 – 4.68 L/ha; Accord®XRT, Dow AgroSciences,

Indianapolis, IN). Glyphosate was applied to reduce plant competition prior to disking

and broadcast seeding of switchgrass.

Three permanent sampling points, generated during previous studies conducted on

these experimental stands (e.g. Loman et al. 2014), were located along the southeastern to northwestern corners of the experimental stands, with end points ≥ 50 m from edges to

reduce edge effects. Permanent points were also arranged to maximize distances from

streamside management zones (pine/hardwood and hardwood corridors maintained along

waterways). I randomly generated four paired points within a 50 m radius of the three

permanent sampling points per treatment (24 points per treatment). Paired points allowed

stratification of sampling points by beds (planted pines) and inter-bed rows (either scrub- shrub vegetation or switchgrass). Monocultures lacked beds and inter-bed rows, with

sampling instead conducted at four unpaired points (12 points per treatment). I sampled

arthropods three times annually from late May to late June, 2014 – 2015, with one

sampling event occurring in May and two in June. This period was selected as it

coincided with breeding and nesting period of avian species.

I sampled arthropods using heavy duty, 38.1cm diameter sweep-nets with a

91.4cm handle ( BioQuip Products, Rancho Dominguez, California, USA), as this is the optimal method for collecting arthropods associated with medium height vegetation (e.g. shrubs and saplings; Ozanne 2005), which was typical of my study sites. I collected arthropod samples when the vegetation was dry and wind speeds were < 20km/h, as these are optimal conditions for effective capture of arthropods using sweep-nets (Doxon et al.

2011). Only one person collected samples during each sampling event to reduce bias associated with using multiple observers (Buffington and Redak 1998). Sweeps of the net were consistent among treatment types, with the net reaching a maximum height of 3 m

with the arc (approx. 2 m wide) ending at ground level. At the end of each sweep, I

twisted the net 180° to prevent escapes (Doxon et al. 2011). I placed collected samples

into a re-sealable plastic bag and left them in a kill bucket (i.e. five gallon bucket

containing sponges soaked in acetone) until storage by freezing was available (Doxon et

al. 2011). I identified all arthropods to order using the dichotomous key of Triplehorn and

Johnson (2005).

Statistical Analysis

I calculated Shannon’s Diversity Index, richness, and evenness to assess arthropod community responses to intercropping and planting monocultures of switchgrass within loblolly pine plantations compared to loblolly pine stands following standard management practices (R package “vegan”; R Core Team 2013, Oksanen et al.

2011). I used linear mixed effects models following a normal distribution to compare community metrics among treatments. Models consisted of a fixed effect of treatment and un-nested random effects of year, plot, and visit. I assessed community metrics for 11 of 13 detected arthropod orders, which included Acari, Araneae, Coleoptera, Diptera,

Hemiptera, Hymenoptera, Lepitoptera, Mantodea, Neuroptera, Opiliones, and Orthoptera.

I did not include Decapoda and Phasmatodea in diversity analyses due to minimal detections of these orders throughout the study (n = 2 and n = 1, respectively). I conducted a post-hoc Tukey test (R package “multcomp”) with one degree of freedom linear contrasts to compare mean diversity, richness, and evenness among treatments

(Hothorn et al. 2008).

I used generalized linear mixed effects models (R package “lme4”) following a poisson distribution to assess response of arthropod general abundance to intercropping and planting monocultures of switchgrass compared to loblolly pine stands following standard management practices (R Core Team 2013, Douglas et al. 2015). The models consisted of a fixed effect of treatment and un-nested random effects of year, plot, and visit. I used a post-hoc Tukey test (R package “multcomp”) with one degree of freedom

linear contrasts to compare mean abundance of arthropods across treatments (Hothorn et

al. 2008). I selected five arthropod orders (Araneae, Coleoptera, Diptera, Hemiptera, and

Orthoptera) for analyses to assess general abundance response to treatments, based on the criteria that each order had a sufficient number of detections (n = > 50) across all

treatments. I considered all tests significant at α = 0.05.

Results

I detected 2,913 individuals (n = 1,172 and 1,741 in 2014 and 2015, respectively),

encompassing 13 orders over the 2-year sampling period (2014 – 2015; Table 2.1).

Diversity significantly differed between switchgrass intercropped and pine control treatments (z-value = -2.62, P = 0.023), and between switchgrass monoculture and pine

control treatments (z-value = -4.92, P = <0.001). Diversity did not significantly differ

between switchgrass monoculture and switchgrass intercropped treatments (z-value = -

2.30, P = 0.055). Richness significantly differed between switchgrass monoculture and

pine control treatments (z-value = -4.13, P = <0.001), and between switchgrass

monoculture and switchgrass intercropped treatments (z-value = -3.18, P = 0.004).

Richness did not differ between switchgrass intercropped and pine control treatments (z-

value = 0.94, P = 0.61). Evenness significantly differed between switchgrass intercropped

and pine control treatments (z-value = -2.49, P = 0.033), and between switchgrass

monoculture and pine control treatments (z-value = -2.35, P = 0.049). Evenness did not

significantly differ between switchgrass monoculture and switchgrass intercropped

treatments (z-value = 0.029, P = 0.98; see Table 2.2).

Araneae and Coleoptera general abundance followed a similar pattern, with

abundances differing significantly between switchgrass monoculture and pine control

treatments and between switchgrass monoculture and switchgrass intercropped treatments

(Table 2.3). Diptera general abundance differed significantly between switchgrass 13

intercropped and pine control treatments (z-value = -2.60, P = 0.024) and between switchgrass monoculture and pine control treatments (z-value = -3.85, P = <0.001), but not between switchgrass monoculture and switchgrass intercropped treatments (z-value =

-1.32, P = 0.38). Hemiptera general abundance differed significantly between switchgrass intercropped and pine control treatments (z-value = 2.49, P = 0.034), with no significant differences being observed among the remaining treatment comparisons. Orthoptera general abundance was significantly different between switchgrass monoculture and pine control treatments (z-value = 3.65, P = 0.00083), with no significant differences being observed among the remaining treatment comparisons (Table 2.3).

Discussion

Results of my study indicated that cultivation of switchgrass, whether intercropped or planted in a monoculture within loblolly pine plantations, led to a significant reduction in arthropod diversity and evenness. My results also indicate that arthropod richness was significantly reduced in switchgrass monoculture treatments as compared to switchgrass intercropped and pine control treatments. Responses of

arthropod diversity, richness, and evenness to intercropping and planting monocultures of

switchgrass indicated that arthropod communities responded negatively to these treatments as compared to pine control treatments, four and five years post-stand establishment. Furthermore, general abundance responses to treatments varied across arthropod orders. For example, I detected higher (Orthoptera and Hemiptera) and lower

(Diptera) abundances in treatments containing switchgrass, compared to treatments without switchgrass.

Multiple taxonomic groups respond to changes in the structural and compositional diversity of vegetative communities (MacArthur and MacArthur 1961, Tews et al. 2004 and citations therein). Iglay et al. (2012a) hypothesized that intercropping switchgrass

may increase diversity by providing a heterogeneous plant community consisting of a

herbaceous component in inter-bed rows and a woody, shrub component in pine beds.

However, my study indicated that structural and compositional diversity of the plant

community in switchgrass intercropped treatments reduced arthropod community

metrics. I hypothesize that the decline in arthropod community metrics had less to do

with structural and compositional heterogeneity of the plant community of switchgrass

intercropped treatments, but instead was influenced by specific habitat requirements of

the arthropods detected (Tews et al. 2004).

Separately, loblolly pine plantations and switchgrass plantings are able to support

diverse arthropod communities (e.g. Bird et al. 2004, Gardiner et al. 2010, Landis and

Werling 2010, Iglay et al. 2012b). However, specific habitat requirements of certain

arthropods associated with loblolly pine plantations may inhibit their use of switchgrass

plantings, and vice-versa (e.g. Martin and Major 2001). My assessment of arthropods was

conducted across two structurally and compositionally differing vegetative communities

(e.g. grassland-forest matrix; Iglay et al. 2012a). These differences in the vegetative

community provide habitat conditions for a different suite of arthropods, resulting in a

shift in the community as amount of available switchgrass changes across treatments. The

observed increase in general abundance of Hemiptera and Orthoptera in switchgrass

intercropped and switchgrass monoculture treatments, respectively, compared to pine

control treatments suggests that some members of these orders may be generalists.

Therefore, they may be able to exploit resources available in vegetative communities associated with switchgrass intercropped and switchgrass monoculture treatments, whereas, other orders detected may have strict habitat requirements, limiting their use of switchgrass plantings (e.g. Rand and Louda 2006).

The inferences made in my study regarding arthropod community response to intercropping switchgrass within loblolly pine plantations are limited. My study does not capture how the entire arthropod community is responding to implementing this novel land use practice. To better elucidate response of the overall arthropod community, future research should incorporate multiple sampling techniques. Sweep-net sampling is the optimal technique used to assess arthropods associated with medium-height vegetation, such as grasses and small shrubs (Ozanne 2005). However, sweep-net sampling may not be the optimal technique for sampling large, dense thickets of thorny shrubs (e.g. Rubus argutus), which dominated my study site (e.g. Iglay et al. 2012a, Wheat 2015). Coupling multiple sampling techniques, such as sweep-nets, pit-fall traps, and branch clipping, would allow for a more extensive sampling of the arthropod community (Ozanne 2005,

Woodcock 2005). Additionally, a sampling period encompassing a large portion of the year should be implemented to evaluate effects of switchgrass intercropping on seasonal patterns exhibited by some arthropods (e.g. Pinheiro et al. 2002, Danks 2007). Lastly, future studies should evaluate how intercropping switchgrass affects arthropods identified to a lower taxonomic level, such as family. This would allow for greater delineation of arthropod functional roles and habitat requirements, improving our understanding of arthropod response to intercropping switchgrass.

Arthropods provide valuable ecosystem services, such as pest control, pollination, and decomposition, with the annual value of these services estimated to be worth $57 billion (Lousey and Vaughan 2006). Arthropods are also important food resources for other taxonomic groups, such as amphibians, small mammals, and birds (e.g. Hamilton

1941, Holmes and Schultz 1988, Moseley et al. 2005, Horn and Hanula 2008). Therefore, it is vital to understand how forest management practices influence arthropod communities and, in turn, limit or enhance ecosystem services and biodiversity.

Arthropod communities respond differently to the implementation of novel forestry practices across different geographic regions and forest types (e.g. Bird et al. 2004, Horn and Hanula 2008, Ulyshen and Hanula 2009). It is currently unknown how intercropping switchgrass within forest stands of differing ages, other forests types, and different geographic regions will impact arthropod communities. Comparative and more extensive studies are needed to provide greater insight regarding the impacts of this novel land use practice.

Management Implications

Observations made from my study indicate that intercropping switchgrass within

loblolly pine plantations may negatively affect arthropod diversity and evenness as

compared to pine stands following typical management practices. It is also clear that

abundance responses to intercropping switchgrass varies across orders, with positive

responses detected in switchgrass intercropped treatments compared to pine control

treatments, and vice-versa. Although past research reveals that certain management

practices within loblolly pine plantations can benefit arthropods, it appears that, overall,

intercropping switchgrass provides no additional benefits (e.g. Ulyshen and Hanula 2009, 17

Iglay et al. 2012b). In fact, it appears that switchgrass intercropping may negatively affect

the arthropod community associated with loblolly pine stands following typical

silviculture practices, four and five years post-stand establishment. However, inferences

drawn from this study are limited due to its temporal scope, but it does provide a basis for

continued research aimed at addressing arthropod responses to intercropping switchgrass

within loblolly pine plantations.

Negative impacts of switchgrass establishment to arthropod communities could

have important ramifications on the ecosystem services provided by arthropods and on

wildlife species dependent on arthropods as a prey base. Additional research is needed to

evaluate potential negative effects of switchgrass intercropping on arthropod

communities. Continued research is also needed regarding effects of intercropping

switchgrass from stand establishment to three years post stand establishment and beyond five years post stand establishment. Lastly, additional research is needed to address how different establishment practices, such as coarse woody debris removal associated with intercropping switchgrass, affects arthropod communities compared to establishment practices currently implemented on non-intercropped pine. Addressing the

aforementioned gaps in research regarding arthropod community response to

intercropping switchgrass is needed before a recommendation can be made regarding

viability of intercropping switchgrass within loblolly pine plantations.

Table 2.1 Mean and standard deviation of arthropod abundance among treatments established within an intensively managed loblolly pine forest and summed across years (2014 – 2015) in Kemper County, Mississippi, USA.

Order Switchgrass Switchgrass Pine Control Intercropped Monoculture Acari 0.20 ± 0.60 NP 0.70 ± 1.63 Araneae 15.10 ± 8.27 8.90 ± 2.55 14.70 ± 9.31 Coleoptera 7.70 ± 3.02 3.10 ± 2.23 5.70 ± 3.88 Decapoda NP NP 0.20 ± 0.63 Diptera 5.20 ± 4.78 3.70 ± 3.77 9.10 ± 5.42 Hemiptera 46.40 ± 17.62 38.70 ± 24.26 28.50 ± 9.69 Hymenoptera 1.20 ± 0.78 0.50 ± 0.70 1.40 ± 1.35 Lepidotpera 0.80 ± 0.91 0.20 ± 0.42 1.00 ± 0.66 Mantodea 0.10 ± 0.31 NP 1.00 ± 1.33 Neuroptera 0.60 ± 0.84 0.10 ± 0.31 0.20 ± 0.42 Opiliones 0.60 ± 0.96 NP 0.70 ± 1.05 Orthoptera 8.20 ± 2.65 11.20 ± 6.92 5.70 ± 3.49 Phasmatodea NP 0.10 ± 0.31 NP NP: Not Present

Table 2.2 Linear tests of hypotheses of arthropod diversity, richness, and evenness among treatments established within a loblolly pine plantation in Kemper County, Mississippi, USA, 2014 – 2015.

Linear Effect Size CI Lower CI Upper z-value P-value Hypotheses Diversity IC --- PC -0.16 -0.30 -0.01 -2.63 0.02 M --- PC -0.31 -0.45 -0.16 -4.92 <0.001 M --- IC -0.14 -0.28 0.002 -2.30 0.06 Richness IC --- PC -0.26 -0.92 0.39 -0.94 0.61 M --- PC -1.16 -1.82 -0.50 -4.13 <0.001 M --- IC -0.90 -1.56 -0.23 -3.18 0.004 Evenness IC --- PC -0.07 -0.14 -0.004 -2.49 0.03 M --- PC -0.06 -0.13 -0.0002 -2.35 0.04 M --- IC -0.004 -0.06 0.07 0.14 0.98 IC: Switchgrass intercropped PC: Pine control M: Switchgrass monoculture ---: Signifies a comparison between treatments

Table 2.3 Linear tests of hypotheses of Araneae, Coleoptera, Diptera, Hemiptera, and Orthoptera abundance among treatments within a loblolly pine plantation in Kemper County, Mississippi, USA, 2014 – 2015.

Linear Effect Size CI Lower CI Upper z-value P-value Hypotheses Araneae IC --- PC 0.02 -0.33 0.39 0.17 0.98 M --- PC -0.49 -0.89 -0.09 -2.91 0.009 M --- IC -0.52 -0.92 -0.12 -3.09 0.005 Coleoptera IC --- PC 0.31 -0.20 0.82 1.42 0.32 M --- PC -0.60 -1.20 -0.0004 -2.34 0.04 M --- IC -0.91 -1.49 -0.33 -3.67 <0.001 Diptera IC --- PC -0.57 -1.08 -0.05 -2.60 0.02 M --- PC -0.90 -1.45 -0.35 -3.85 <0.001 M --- IC -0.33 -0.92 0.25 -1.32 0.38 Hemiptera IC --- PC 0.48 0.02 0.93 2.49 0.03 M --- PC 0.23 -0.22 0.69 1.21 0.44 M --- IC -0.24 -0.69 0.20 -1.27 0.41 Orthoptera IC --- PC 0.36 -0.08 0.81 1.89 0.14 M --- PC 0.67 0.24 1.10 3.65 <0.001 M --- IC 0.30 -0.08 0.70 1.82 0.16 IC: Switchgrass intercropped PC: Pine control M: Switchgrass monoculture ---: Signifies a comparison between treatments

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CHAPTER III

BREEDING BIRD RESPONSE TO INTERCROPPING SWITCHGRASS WITHIN A

LOBLOLLY PINE PLANTATION

Introduction

Cellulosic biomass production may exacerbate current conservation threats to agricultural and grassland associated bird species (Fargione et al. 2008, Robertson et al.

2012). Switchgrass plantings have been shown to support diverse avian communities, however, studies have focused mainly on switchgrass plantings within regions historically dominated by grasslands and not on cultivating switchgrass within a forest- dominated landscape (Murray and Best 2003, Murray et al. 2003, Roth et al. 2005,

Robertson et al. 2012). With increased global interest in biofuels as a renewable, alternative energy source, a novel land use practice of intercropping switchgrass within loblolly pine plantations has been developed for producing cellulosic biomass (Koh and

Ghazoul 2008, Riffell et al. 2012). This land use practice allows for the co-production of an annual crop of cellulosic biomass and forest products, while circumventing competition for land that is already in production and reducing conversion of natural land to biomass production.

Loblolly pine plantations are a ubiquitous landscape cover of the southeastern

United States, with approximately 5 million acres present within Mississippi (USDA

Forest Service 2007, Wear and Greis 2012). These plantations are able to support a

diverse avian community throughout an entire rotation, from establishment to harvest

(e.g. Childers et al. 1986, Wilson and Watts 2000, Lohr et al. 2002, Iglay 2010, Owens et al. 2014). More specifically, loblolly pine plantations provide habitat conditions for scrub-shrub associated avian species, which have experienced steep population declines

(Brawn et al. 2001, Loman et al. 2014, Ownes et al. 2014). Intercropping switchgrass within loblolly pine plantations results in the removal of inter-bed row scrub-shrub vegetation and replaces it with switchgrass. Limited knowledge currently exists on how alterations to the vegetative assemblage due to intercropping switchgrass will affect scrub-shrub associated avian species within loblolly pine plantations (e.g. Riffell et al.

2012, Loman et al. 2014).

A past study revealed that intercropping switchgrass within loblolly pine plantations supported an avian community as diverse as one associated with loblolly pine managed under standard silviculture practices. However, intercropping switchgrass resulted in a one to two year lag in avian abundance (Loman et al. 2014). Loman et al.

(2014) provides some insight regarding scrub-shrub associated avian species responses to intercropping switchgrass, however, inferences were limited due to the temporal scope of the study (conducted from establishment to three years post establishment). No study has

yet to assess response of scrub-shrub associated avifauna to within stand alterations due

to intercropping switchgrass within loblolly pine stands four and five years post

establishment.

Acting as indicators of ecosystem integrity, the diversity of species and habitat

conditions used, and ease of monitoring make birds well suited for evaluation and

assessment of forest management practices (Maurer 1993, Bibby et al. 2000, Nuttle et al.

2003). Because birds can help elucidate effects of novel forest management practices and

because limited knowledge currently exists regarding birds and intercropping

switchgrass, I investigated scrub-shrub associated breeding bird responses to

intercropping switchgrass within loblolly pine plantations. My objective was to assess

patterns of breeding bird abundance and diversity to intercropping switchgrass within

loblolly pine stands, four and five years post establishment. A secondary objective was to

compare the Conservation Value (CV) of treatments to quantify their value to breeding

birds. I hypothesized that switchgrass intercropping would decrease breeding bird

abundance and diversity compared to loblolly pine stands following typical management

practices. Switchgrass establishment in the inter-bed rows would result in less available

habitat for birds associated with scrub-shrub vegetative communities, which is a common

vegetative assemblage of loblolly pine stands four and five years post establishment

(Iglay et al. 2012a, Foggia 2015).

Materials and Methods

Study Area

I collected bird data in Kemper County, Mississippi, USA (32 51’ N, 88 33’ W)

within the Interior Flatwoods Area of the Upper Coastal Plain (Petty 1977) on property

owned and managed by Weyerhaeuser Company and within research sites established

and maintained by Weyerhaeuser Company and Catchlight Energy LLC (CLE), a joint

venture between Chevron and Weyerhaeuser. The climate of the region was subtropical

with mean annual temperatures of 16° C – 18° C (mean for minimum and maximum) and a mean annual precipitation of 140 cm (National Oceanic and Atmospheric

Administration 2013). The study area consisted of 9,600 ha of loblolly pine stands of 27

various ages (70%), mature pine-hardwoods (17%), hardwoods (10%), and non-forested areas (3%; Iglay 2010).

Study Design

monoculture). Each experimental stand was previously a mature loblolly pine stand

clearcut harvested during 2009 and 2010. Pine control treatment, used Weyerhaeuser

standards for site preparation, competition control, tree planting, and tree spacing. Site

preparation included a V-blade plow, bedding plow, and subsoil ripper to establish pine beds. Planted pine seedlings were spaced 1.5×6.1 m resulting in pine beds and inter-bed rows having widths of 1.2 m and 4.9 m, respectively. A banded application of imazapyr

(0.29 L/ha; Arsenal® AC, BASF Corp., Research Triangle Park, NC) and sulfometuron-

methyl (0.15 L/ha; Oust®, E. I. du Pont de Nemours and Company, Wilmington, DE)

was applied during the first growing season to pine beds to reduce woody and herbaceous

competition. Switchgrass intercropped treatment had similar site preparation as pine

control stands with the addition of more extensive coarse woody debris removal. Once

pine beds were established, a V-blade plow was used to remove coarse woody debris

from inter-bed rows into pine bed edges. Upon clearing inter-bed rows, a banded

application of glyphosate (2.34 – 4.68 L/ha; Accord®XRT, Dow AgroSciences,

Indianapolis, IN) was applied to inter-bed rows. Inter-bed rows were then disked and

broadcast seeded with switchgrass. Switchgrass intercropped stands were seeded in

spring 2011 and reseeded again in 2012 due to poor establishment after initial seeding. 28

Inter-bed rows were sprayed with a banded application of glyphosate and disked a second time during the reseeding event in 2012, Site preparation for switchgrass monoculture

treatment included complete removal of coarse woody debris using a V-blade plow and

broadcast application of glyphosate (2.34 – 4.68 L/ha; Accord®XRT, Dow AgroSciences,

Indianapolis, IN). Glyphosate was applied to reduce plant competition prior to disking

and broadcast seeding of switchgrass.

Three permanent sampling points, generated during previous studies conducted on

these experimental stands (e.g. Loman et al. 2014), were located along the southeastern to northwestern corners of the experimental stands with end points ≥ 50 m from edges to

reduce edge effects. Permanent points were also arranged to maximize distances from

streamside management zones (pine/hardwood and hardwood corridors maintained along

waterways) and minimize overlap of detections from other survey locations. I conducted

ten minute point transect surveys for breeding birds at each of the three permanent points.

For each survey, I recorded all detections made, identified species, method of detection

(visual or auditory), time of detection during the survey, distance from the observer at time of detection, and number of individuals detected. I recorded distances of detected individuals using the consistent spacing (1.5×6.1 m) of planted loblolly pines as a reference for distance estimation. I recorded distances in exact distances and not binned

distances. I conducted surveys between sunrise and 3.5 – 4 hours after sunrise. I did not

conduct surveys in inclement weather conditions (e.g. high winds ((≥ 16.09 kph), rain, and heavy fog) that could influence ability of individuals to be detected or reduce observer’s ability to detect birds. I surveyed all treatment plots five times annually between May and mid-June, 2014 – 2015, coinciding with the avian breeding period,

with a minimum of seven days and a maximum of ten days between surveys of the same treatment plot. This sampling time frame reduced detection of late staying wintering birds and allowed for migrating individuals to reach breeding grounds and establish territories.

Multiple observers were used and rotated evenly among treatment plots to minimize bias associated with multiple observers conducting point transect surveys (MacKenzie et al.

2003). Observers received similar training prior to conducting surveys, which consisted of mock point transects. Training continued until observers were proficient with bird identification and distance estimation.

Statistical Analysis

I used the statistical package “Unmarked” in R to analyze breeding bird abundances obtained from point transect surveys. Within “Unmarked”, I used the distance sampling model “gdistsamp”. I used this statistical package because it accounts for imperfect detections of individuals across treatments and counts (Fisk and Chandler

2011, R Core Team 2013). Abundance estimates were obtained for species that met the specific criteria for analyses, which included having approximately 40 – 50 detections for model convergence and an accurate distance estimate obtained, with this condition excluding coursing birds such as Turkey Vultures (Cathartes aura) and Barn Swallows

(Hirundo rustica) from analysis (Loman et al. 2014). I also excluded species that were solely confined to streamside management zones or associated with adjacent forest stands

(e.g. Tufted Titmouse [Baeolophus bicolor] and Pine Warbler [Setophaga pinus]). Lastly,

switchgrass monocultures did not have an adequate number of detections for model

convergence of any breeding bird species, and so, I excluded these from analyses.

I created a no-covariate model for each breeding bird species and selected the best

key function, which describes the shape of detection function based on observed

distances, using AIC. Once a key function was selected, I built a candidate model for

each species using treatment as an abundance covariate and observer as a detection

covariate. I then used abundance estimates to calculate Shannon’s Diversity Index for

treatments (“vegan” package in R; Oksanen et al. 2011). I used a linear mixed effects

model (“lme4” package in R) to compare breeding bird diversity between switchgrass

intercropped and pine control treatments (Douglas et al. 2015). The model consisted of a

fixed effect of treatment and un-nested random effects of plot and year. I then performed

a post-hoc Tukey test (“multcomp” package in R) with one degree of freedom linear

contrast to compare mean diversity between switchgrass intercropped and pine control

treatments (Hothorn et al. 2008).

I calculated a Conservation Value Index (CV) for each treatment following the

recommendations of Nuttle et al. (2003) and using Partners in Flight (PIF) ranks for the

Southeastern Coastal Plain Conservation Region to calculate weighted means of bird

abundance. Partners in Flight is a partnership of stakeholders, including government agencies, non-governmental organizations, and industry, interested in avian conservation.

Partners in Flight ranks are derived from the relative extinction risk of each species, and are used to prioritize conservation for species of the United States, Canada, and Mexico, with a higher PIF rank indicating a species of higher priority. Partners in Flight rank is assigned based on scores given to assessment factors that include population size and trend (increasing, decreasing, or stable), breeding distribution, non-breeding distribution, and discerned threats to breeding and threats to non-breeding populations (Panjabi et al.

2012). To calculate CV, I multiplied PIF ranks by species abundances, with weighted abundances added across each treatment. I used a linear mixed effects model (“lme4”

package in R) with a fixed effect of treatment and un-nested random effects of plot and

year to compare CV between switchgrass intercropped and pine control treatments

(Douglas et al. 2015). I performed a post-hoc Tukey test (“multcomp” package in R) with

one degree of freedom linear contrasts to compare mean CV between treatments

(Hothorn et al. 2008). I considered tests significant at α = 0.05.

Results

I detected 5,462 individuals of 44 different species, 12 of which I used for analyses based on the aforementioned criteria (Table 3.1). Breeding bird abundance did not significantly differ between switchgrass intercropped and pine control treatments for any of the 12 species. No significant differences were found among observers and their ability to detect each species. I had minimal to no detections of the 12 breeding birds assessed on switchgrass monoculture treatments, with most detections on these

treatments being flyovers. I calculated a Shannon’s Diversity Index for the same 12

species and found that diversity did not significantly differ between pine control and

switchgrass intercropped treatments (z-value = -0.437, P = 0.972). I calculated

Conservation Value (CV) using abundance estimates of the same 12 species, and I found no significant difference in CV between pine control and switchgrass intercropped treatments (z-value = -2.325, P = 0.093). General abundance of Gray Catbirds (Dumetella carolinensis) differed greatly between 2014 and 2015 (n = 2 and n = 62, respectively), and for Orchard Orioles (Icterus spurius) between 2014 and 2015 (n = 4 and n = 20,

respectively). General abundances of each species were summed across pine control and switchgrass intercropped treatments.

Discussion

Intercropping switchgrass within loblolly pine plantations did not influence the breeding bird community associated with scrub-shrub vegetation. Intercropping switchgrass did not reduce breeding bird abundance and diversity compared to pine control treatments as predicted. There are several possible explanations for why breeding bird abundance and diversity did not differ between switchgrass intercropped and pine control treatments. First, the dense scrub-shrub vegetation maintained within pine beds of switchgrass intercropped treatments was analogous to the scrub-shrub vegetation maintained within pine control treatments. Patches of thickets consisting of sawtooth blackberry (Rubus argutus), Japanese honeysuckle (Lonicera japonica), and other woody

plant species were maintained within switchgrass intercropped beds (Iglay et al. 2012a,

Wheat 2015). Retaining these patches of thickets provided habitat conditions to support

scrub-shrub associated breeding birds. Second, implementation of adjacency constraints

to meet forest certification standards produces a heterogeneous landscape that provided a

diversity of habitat conditions (Miller et al. 2009, SFI 2015). Availability of diverse

habitat conditions in adjacent edges and stands within these managed systems may have

offset potential resource limitations associated with switchgrass intercropped treatments

(Zanette et al. 2000, Fahrig et al. 2011).

Though supporting a similar breeding bird community in my study, this trend may

not continue as stands age (Loman et al. 2014). Intercropping switchgrass creates more

open understory conditions, potentially maintaining scrub-shrub habitat conditions longer 33

throughout the rotational period than pine stands following typical silviculture practices

(Riffell et al. 2012). As stands age, breeding bird community structure of switchgrass

intercropped treatments may diverge from that of pine control treatments, similar to the

findings of Loman et al. (2014). As loblolly pine stands age, the canopy closes and

understory vegetation becomes more homogeneous, being dominated by woody shrubs,

such as sawtooth blackberry (Iglay et al. 2012a, Foggia 2015). This results in a reduction

in avian diversity until the understory is re-opened through thinning, prescribed fire, or

herbicide application (Dickson et al. 1993, Wilson and Watts 1999, Iglay 2010).

Intercropping switchgrass may maintain a more open understory and diverse vegetative

community for a longer timeframe than loblolly pine stands of a similar age, following

typical silviculture practices, and thus, support a more diverse breeding bird community

(MacArthur and MacArthur 1961, Tews et al. 2004, Iglay et al. 2012a). Maintaining

scrub-shrub habitat conditions in switchgrass intercropped treatments may create a

potential conservation benefit to scrub-shrub associated birds, which have experienced

population declines (Brawn et al. 2001).

Breeding bird responses to switchgrass monoculture treatments suggests that

these small grasslands provide few resources for breeding scrub-shrub associated birds.

Riffell et al. (2012) hypothesized that switchgrass cultivation within loblolly pine

plantations could serve as a potential conservation benefit to grassland associated

breeding birds. However, detections suggesting a local population of grassland associated

breeding birds were not observed on switchgrass monoculture treatments. Lack of

grassland breeding bird detections may be a result of the small size of the grasslands (~10

ha) and their placement within a forest-dominated landscape (Johnson and Igl 2001,

Robertson et al. 2012). There was one exception, a singing Eastern Meadowlark

(Sturnella magna), a grassland species (Lanyon 1995), was detected throughout the 2015

season. A potential reason for presence of this Eastern Meadowlark is that grassland

associated breeding birds are locating these grasslands within the forest-dominated

landscape, and are starting to use them. Despite a lack of use of these grasslands by

grassland-associated breeding birds, switchgrass monocultures may be important

stopover sites for migrating species, or be used as overwintering areas. Thus, continued

assessment throughout the breeding season and additional assessment outside of the

breeding season of switchgrass monocultures is needed.

It is currently unknown what caused annual variation in abundance of Gray

Catbirds, as this species used habitat conditions readily abundant across the landscape

during both years of this study. The difference detected in abundance of Orchard Orioles

could be attributed to young hardwoods reaching a size and shape that provides adequate

nest sites (Scharf and Kren 2010). Orchard Orioles nest in the forks of trees away from

the main trunk, a condition that is available in a few scattered young hardwoods of the

sampled treatments (e.g. Acer rubrum [red maple] and Liquidambar styraciflua

[sweetgum]). Availability of these trees may relate more to stand age, with more

hardwoods available as stands mature, and less so with the treatment being implemented

(e.g. switchgrass intercropped or pine control), but further study is needed before a

definitive answer can be drawn.

Avian communities respond differently to implementing novel forestry

management practices within loblolly pine plantations (e.g. Wilson and Watts 1999, Lohr

et al. 2002, Iglay 2010, Iglay et al. 2012b, Loman et al. 2014, Owens et al. 2014).

Additional research on effects of intercropping switchgrass should evaluate movement of individuals within treatment plots and within adjacent forest stands. This would provide insight into territory size between treatments and if it is influenced by potential differences in resource availability (Myers et al. 1979, Marshall and Cooper 2004). Also, this would make clear whether individuals are using adjacent edges and stands to offset resource limitations in switchgrass intercropped treatments (Zanette et al. 2000, Fahrig et al. 2011). It is currently unknown how intercropping switchgrass within older forest stands, other forests types, and different geographic regions will affect breeding bird communities. Comparative and more extensive studies are also needed to provide greater insight regarding these effects.

Management Implications

Observations made from my study indicate that intercropping switchgrass within loblolly pine plantations supported a scrub-shrub associated breeding bird community similar to one present in pine stands following typical silviculture practices. If co-

producing forest products and cellulosic biomass, while conserving scrub-shrub breeding

bird habitat are management goals, forest managers should implement switchgrass

intercropping within loblolly pine plantations. However, this recommendation is limited

to stands four and five year post establishment, given the scope of my study. Due to the

limited temporal scope of this study, it is unknown how intercropping switchgrass affects breeding bird communities as stands age. Continued research is needed in this regard.

Also, an assessment of intercropping switchgrass during the non-breeding period is needed before a holistic recommendation can be made. Switchgrass monocultures did support a diverse breeding bird community in my study. 36

Table 3.1 Mean and standard deviation of breeding birds detected per treatment and summed across years (2014 – 2015) within a loblolly pine plantation in Kemper County, Mississippi, USA.

Species Switchgrass Intercropped Pine Control

Brown-headed Cowbird 5.60 ± 2.80 6.80 ± 4.47 Molothrus ater Common Yellowthroat 16.70 ± 6.25 17.90 ± 6.10 Geothlypis trichas Eastern Towhee 13.60 ± 3.57 13.20 ± 5.01 Pipilo erythrophthalmus Gray Catbird 2.70 ± 2.91 3.70 ± 4.69 Dumetella carolinensis Indigo Bunting Passerina 24.60 ± 5.82 19.20 ± 7.12 cyanea Northern Bobwhite 1.60 ± 2.12 1.60 ± 2.41 Colinus virginianus Northern Cardinal 4.40 ± 1.96 5.90 ± 3.04 Cardinalis cardinalis Northern Mockingbird 2.40 ± 1.90 1.60 ± 1.35 Mimus polyglottos Orchard Oriole 0.90 ± 1.37 1.50 ± 1.35 Icterus spurius Prairie Warbler 31.40 ± 4.30 34.40 ± 7.92 Setophaga discolor White-eyed Vireo 12.00 ± 4.88 17.30 ± 6.46 Vireo griseus Yellow-breasted Chat 47.80 ± 6.16 48.00 ± 3.46 Icteria virens Switchgrass monocultures had no detections, and therefore, are not included.

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Brawn, J.D., S.K. Robinson, and F.R. Thompson III. 2001. The role of disturbance in the ecology and conservation of birds. Annual Review of Ecology and Systematics 32: 251 – 276.

Childers, E.L., T.L. Sharik, and C.S. Adkisson. 1986. Effects of loblolly pine plantations on songbird dynamics in the Virginia Piedmont. The Journal of Wildlife Management 3: 406 – 413.

Dickson, J.G., R.N. Conner, and J.H. Williamson. 1993. Winter birds in a developing pine plantation. Proceedings of the Annual Conference of Southeastern Association of Fish and Wildlife Agencies 49: 303 – 313.

Douglas, B., M. Maechler, B. Bolker, and S. Walker. 2015. Fitting linear mixed-effects models using lme4. Journal of Statistical Software 67: 1 – 48.

Fahrig, L., J. Baudry, L. Brotons, F.G. Burel, T.O. Crist, R.J. Fuller, C. Sirami, G.M. Siriwardena, and J. Martin. 2011. Functional landscape heterogeneity and animal biodiversity in agricultural landscapes. Ecology Letter 14: 101 – 112.

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Foggia, J.R. 2015. Implications of stand adjacency and edge for birds in a managed forest ecosystem. Thesis, Mississippi State University, Starkville, USA.

Hothorn, T., F. Bretz, and P. Westfall. 2008. Simultaneous Inference in General Parametric Models. Biometric Journal 50: 346 – 363.

Iglay, R.B., S. Demarais, T.B. Wigley, and D.A. Miller. 2012b. Bird community dynamics and vegetation relationships among stand establishment practices in intensively managed pine stands. Forest Ecology and Management 283: 1 – 9.

Johnson, D.H. and L.D. Igl. 2001. Area requirements of grassland birds: A regional perspective. The Auk 118: 24 – 34.

Koh, L.P. and J. Ghazoul. 2008. Biofuels, biodiversity, and people: Understanding the conflicts and finding opportunities. Biological Conservation 141: 2450 – 2460.

Lanyon, W.E. 1995. Eastern Meadowlark (Sturnella magna). In The Birds of North America, No. 160 (A. Poole and F. Gill, eds.). The Birds of North America Online, Ithaca, New York, USA.

Lohr, S.M., S.A. Gauthreaux, and J.C. Kilgo. 2002. Importance of coarse woody debris to avian communities in loblolly pine forests. Conservation Biology 16: 767 – 777.

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Marshall, M.R. and R.J. Cooper. 2004. Territory size of a migratory songbird in response to caterpillar density and foliage structure. Ecology 85: 432 – 445.

Maurer, B.A. 1993. Biological diversity, ecological integrity, and neotropical migrants: New perspectives for wildlife management. Pages 24 – 31 in D.M. Finch and W. Peter, editors. Status and management of neotropical migratory birds. United States Forest Service, General Technical Report SO-65, Washington, D.C., USA.

Miller, D.A., T.B. Wigley, and K.V. Miller. 2009. Managed forests and conservation of terrestrial biodiversity in the southern United States. Journal of Forestry 107: 197 – 203.

Murray, L.D. and L.B. Best. 2003. Short-term bird response to harvesting switchgrass for biomass in Iowa. The Journal of Wildlife Management 67: 611 – 621.

Murray, L.D., L.B. Best, T.J. Jacobsen, and M.L. Braster. 2003. Potential effects on grassland birds of converting marginal cropland to switchgrass biomass production. Biomass and Bioenergy 25: 167 – 175.

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Owens, F.L., P.C. Stouffer, M.J. Chamberlain, and D.A. Miller. 2014. Early-successional breeding bird communities in intensively managed pine plantations: Influence of vegetation succession but not site preparations. Southeastern Naturalist 13: 423 – 443.

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Riffell, S., J. Verschuyl, D. Miller, and T.B. Wigley. 2012. Potential biodiversity response to intercropping herbaceous biomass crops on forest lands. Journal of Forestry 110: 42 – 47.

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CHAPTER IV

GENERAL CONCLUSIONS

Under current silviculture practices, loblolly pine (Pinus taeda) plantations of the southeastern United States are biologically diverse, supporting species associated with a wide range of habitat conditions (e.g. Wilson and Watts 2000, Horn and Hanula 2008,

Miller et al. 2009, Iglay 2010, Riffell et al. 2012). Maintenance of biological diversity within these systems is an integral aspect of forest management targeted to meet biodiversity measures set by sustainable forestry programs, such as the Sustainable

Forestry Initiative (Miller et al. 2009, Sustainable Forestry Initiative Inc. 2010).

Development of a novel land use practice of intercropping switchgrass (Panicum virgatum) within loblolly pine plantations presents a unique opportunity to evaluate effects of further land use intensification on floral and faunal communities (Riffell et al.

2012). Minimal literature currently exists regarding floral and faunal responses to this

novel land use practice (e.g. Iglay et al. 2012, Homyack et al. 2013, Homyack et al. 2014,

Loman et al. 2014, Wheat 2015). The literature that currently exists is limited by its

temporal scope, with most research focused on young stands (1 – 3 years post

establishment). This study adds to the current body of literature regarding floral and

faunal responses to intercropping switchgrass by evaluating arthropod, an

underrepresented taxonomic group with regards to intercropping switchgrass research,

and breeding bird responses to intercropping switchgrass within older stands (four and five years post establishment).

In my study, intercropping switchgrass provided habitat for breeding bird species associated with scrub-shrub vegetative communities. However, this land use practice

negatively impacted arthropods, an important prey base for some wildlife, including

breeding birds (e.g. Hamilton 1941, McCracken and Tallowin 2004, Horn and Hanula

2008, Moseley et al. 2008). Breeding birds detected in this study included insectivores,

such as Yellow-breasted Chat (Icteria virens), Common Yellowthroat (Geothlypis

trichas), Prairie Warbler (Setophaga discolor), Gray Catbird (Dumetella carolinensis),

and White-eyed Vireo (Vireo griseus; Cimprich and Moore 1995, Hopp et al. 1995,

Guzzy and Ritchison 1999, Nolan et al. 1999, Eckerle and Thompson 2001), yet no

decline in abundance of these species was detected despite potential prey base reductions,

with the caveat that the arthropod community was not entirely sampled due to limitations

of sweep-netting scrub-shrub vegetation. Some breeding birds may be able to supplement their diet with fruit available within intercropped stands, such as Yellow-breasted Chats and Gray Catbirds; however, species that are strictly insectivores (i.e. Prairie Warblers) do not have an alternate food source (Cimprich and Moore 1995, Nolan et al. 1999,

Eckerle and Thompson 2001).

This suggests that arthropods preyed upon are not reduced to a level within

intercropped switchgrass that negatively affected insectivorous breeding birds, or that

breeding birds were able to obtain resources in adjacent edges and stands to offset

resource limitations within switchgrass intercropped stands (Zanette et al. 2000, Fahrig et

al. 2011). Additional research should address movement of breeding birds within

treatment plots and within adjacent forest stands, which would provide insight into

effects of resource availability on territory size and use of adjacent forest edges and

stands (Myers et al. 1979, Marshall and Cooper 2004). Additionally, future research

should examine relationships between arthropod community structure and ecosystem

services (i.e. pollination) and wildlife (e.g. amphibians, other arthropods, small-

mammals) dependent on arthropods as a prey base within intercropped stands (e.g.

Moseley et al. 2008, Losey and Vaughan 2006).

To provide a holistic evaluation of intercropping switchgrass within loblolly pine,

continued study throughout an entire rotational period is needed. Current research is

limited temporally, with research only conducted from stand establishment to five years

post establishment, and taxonomically, with some taxa not represented throughout

entirety of stand existence (e.g. arthropods). Sampling outside of the breeding season for

birds is needed to understand how intercropping switchgrass affects migrating and

overwintering birds. Arthropods should also be studied outside of the avian breeding

period as community structure fluctuates throughout the year (Danks 2007). It is

currently unknown how intercropping switchgrass within older forest stands, other forests

types, and different geographic regions will impact arthropod and breeding bird

communities. Comparative and more extensive studies are needed to provide greater

insight regarding effects of intercropping switchgrass, as this land use practice has

potential to provide economic (e.g. co-production of biomass for biofuels and wood

products) and ecological benefits to society (e.g. carbon sequestration and protection of

water quality; Wigley et al. 2000, Miller et al. 2009).

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